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AND_INDX and AND_INDY implemented

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jborza 2019-04-14 21:25:23 +02:00
parent 8dcea919ed
commit 4bfeb62112
1 changed files with 28 additions and 42 deletions
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70
cpu.c
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@ -70,6 +70,7 @@ word read_word(State6502 * state, word address) {
}
byte get_byte_zero_page(State6502 * state) {
//8 bit addressing, only the first 256 bytes of the memory
byte address = pop_byte(state);
return state->memory[address];
}
@ -86,20 +87,41 @@ byte get_byte_zero_page_y(State6502 * state) {
byte get_byte_absolute(State6502 * state)
{
//absolute indexed, 16 bits
word address = pop_word(state);
return state->memory[address];
}
byte get_byte_absolute_x(State6502 * state) {
//absolute added with the contents of x register
word address = pop_word(state) + state->x;
return state->memory[address];
}
byte get_byte_absolute_y(State6502 * state) {
//absolute added with the contents of y register
word address = pop_word(state) + state->y;
return state->memory[address];
}
byte get_byte_indirect_x(State6502 * state) {
//pre-indexed indirect with the X register
//zero-page address is added to x register
byte indirect_address = pop_byte(state) + state->x;
//pointing to address of a word holding the address of the operand
word address = read_word(state, indirect_address);
return state->memory[address];
}
byte get_byte_indirect_y(State6502 * state) {
//post-indexed indirect
//zero-page address as an argument
byte indirect_address = pop_byte(state);
//the address and the following byte is read as a word, adding Y register
word address = read_word(state, indirect_address) + state->y;
return state->memory[address];
}
int emulate_6502_op(State6502 * state) {
byte* opcode = &state->memory[state->pc++];
switch (*opcode) {
@ -117,8 +139,8 @@ int emulate_6502_op(State6502 * state) {
case AND_ABS: AND(state, get_byte_absolute(state)); break;
case AND_ABSX: AND(state, get_byte_absolute_x(state)); break;
case AND_ABSY: AND(state, get_byte_absolute_y(state)); break;
case AND_INDX: unimplemented_instruction(state); break;
case AND_INDY: unimplemented_instruction(state); break;
case AND_INDX: AND(state, get_byte_indirect_x(state)); break;
case AND_INDY: AND(state, get_byte_indirect_y(state)); break;
case ASL_ACC: unimplemented_instruction(state); break;
case ASL_ZP: unimplemented_instruction(state); break;
case ASL_ZPX: unimplemented_instruction(state); break;
@ -200,26 +222,8 @@ int emulate_6502_op(State6502 * state) {
case LDA_ABS: LDA(state, get_byte_absolute(state)); break;
case LDA_ABSX: LDA(state, get_byte_absolute_x(state)); break;
case LDA_ABSY: LDA(state, get_byte_absolute_y(state)); break;
case LDA_INDX:
{
//pre-indexed indirect
//zero-page address is added to x register
byte indirect_address = pop_byte(state) + state->x;
//pointing to address of a word holding the address of the operand
word address = read_word(state, indirect_address);
LDA(state, state->memory[address]);
break;
}
case LDA_INDY:
{
//post-indexed indirect
//zero-page address as an argument
byte indirect_address = pop_byte(state);
//the address and the following byte is read as a word, adding Y register
word address = read_word(state, indirect_address) + state->y;
LDA(state, state->memory[address]);
break;
}
case LDA_INDX: LDA(state, get_byte_indirect_x(state)); break;
case LDA_INDY: LDA(state, get_byte_indirect_y(state)); break;
case LDX_IMM: unimplemented_instruction(state); break;
case LDX_ZP: unimplemented_instruction(state); break;
case LDX_ZPY: unimplemented_instruction(state); break;
@ -241,26 +245,8 @@ int emulate_6502_op(State6502 * state) {
case ORA_ABS: ORA(state, get_byte_absolute(state)); break;
case ORA_ABSX: ORA(state, get_byte_absolute_x(state)); break;
case ORA_ABSY: ORA(state, get_byte_absolute_y(state)); break;
case ORA_INDX: //ORA, indirect, x
{
//pre-indexed indirect
//zero-page address is added to x register
byte indirect_address = pop_byte(state) + state->x;
//pointing to address of a word holding the address of the operand
word address = read_word(state, indirect_address);
ORA(state, state->memory[address]);
break;
}
case ORA_INDY: //ORA, indirect, y (post_indexed)
{
//post-indexed indirect
//zero-page address as an argument
byte indirect_address = pop_byte(state);
//the address and the following byte is read as a word, adding Y register
word address = read_word(state, indirect_address) + state->y;
ORA(state, state->memory[address]);
break;
}
case ORA_INDX: ORA(state, get_byte_indirect_x(state)); break;
case ORA_INDY: ORA(state, get_byte_indirect_y(state)); break;
case ROL_ACC: unimplemented_instruction(state); break;
case ROL_ZP: unimplemented_instruction(state); break;
case ROL_ZPX: unimplemented_instruction(state); break;